To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 65-nm node by the ArF lithography has been implemented in a mass scale. Manufacturing of 45-nm node devices by the next generation ArF immersion lithography is approaching to the verge of high-volume application. The candidates for the next generation 32-nm node include ultra-high NA lens immersion lithography using a liquid having a higher refractive index than water in combination with a high refractive index lens and a high refractive index resist film, extreme ultraviolet (EUV) lithography of 13.5 nm wavelength, and double patterning version of the ArF lithography, on which active research efforts have been made.
Besides the positive tone resist by alkaline development, a highlight is recently put on the negative tone resist by organic solvent development. It would be desirable if a very fine hole pattern, which is not achievable with the positive tone, is resolvable through negative tone exposure. To this end, a positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern. An attempt to double a resolution by combining two developments, alkaline development and organic solvent development is under study.
As the ArF resist composition for negative tone development with organic solvent, positive ArF resist compositions of the prior art design may be used. Such pattern forming processes are described in Patent Documents 1 to 3.
Independent of whether the resist material is subject to positive or negative tone development, methacrylate unit having an acid labile group is one of predominant constituent units relating to the basic function of the base resin in current chemically amplified resist materials. Likewise, lactone unit is an important unit that governs performance factors during resist pattern formation such as adhesion of base resin film to substrate. Heretofore, methacrylates of monocyclic lactone type such as butyrolactone ring or valerolactone ring and methacrylates of fused ring lactone units as typified by methacrylates of norbornane lactone have been proposed as disclosed in Patent Documents 4 to 6. Sultone units of cyclic sulfonic acid ester structure are also used for the same purpose as the lactone units (see Patent Document 7).
To meet the further miniaturization requirement, there is a desire to have a base resin unit capable of forming a fine size pattern of good profile with improved properties such as control of acid diffusion length and low roughness.